This invention relates to the preparation of alpha, beta-unsaturated aldehydes by reacting formaldehyde with a reactant aldehyde of the formula RCH.sub.2 CHO wherein R is a member of the class consisting of --H, --alkyl, --aryl, --aralkyl, --cycloalkyl, and --alkylaryl radicals, the number of carbon atoms in R being preferably from 1 to 18.
It is well-known that unsaturated aldehydes can be prepared by condensing two aldehydes over a suitable catalyst. This invention relates to a process for preparing unsaturated aldehydes, e.g., acrolein, methacrolein, ethacrolein and the like, by condensing two aldehydes, one of which is formaldehyde, the other aldehyde of formula RCH.sub.2 CHO containing two hydrogens on the alpha carbon, in the presence of a catalyst comprising a borosilicate crystalline molecular sieve, designated as AMS-1B. The catalyst has the following composition in terms of mole ratios of oxides: EQU 0.9.+-.0.2M.sub.2/n O:B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O
wherein M is at least one cation, n is the valence of the cation, Y is a value within the range of 4 to about 600, and Z is a value within the range of 0 to about 160, and providing a specific X-ray diffraction pattern.
Unsaturated aldehydes, such as acrolein, methacrolein, ethacrolein and the like, are widely used for the production of glycerol, polymers and copolymers, pharmaceuticals, herbicides and other compounds of considerable utility. Various processes and catalysts have been proposed for the preparation of unsaturated aldehydes by an aldol-type reaction. Generally, the reaction of the two aldehydes takes place in the vapor or gas phase in the presence of a basic catalyst.
Various catalysts have been proposed for such reaction. For example, U.S. Pat. No. 2,639,295 to Hagemeyer teaches the preparation of unsaturated aldehydes such as acrolein, methacrolein and the like by condensing formaldehyde with aliphatic aldehydes in the presence of an ammonium salt or the salt of a primary or secondary amine. Preferred catalysts are secondary amine hydrogen halides. A molar excess of a second aldehyde in the ratio of usually 1:5 is taught wherein formaldehyde or acetaldehyde is reacted with the second aldehyde to obtain conversions of formaldehyde of 34.0 to 92.5%. U.S. Pat. Nos. 3,573,702 and 3,701,798 to Snapp, et al. teach a process for producing alpha, beta-unsaturated aldehydes which comprises contacting formaldehyde and a saturated aldehyde in the vapor phase in the presence of a solid catalyst comprising a supported rare earth metal oxide of the lanthanide series, the support being any inert material such as alumina or kieselguhr but which is preferably silica gel. A molar ratio of formaldehyde to an excess of the second aldehyde is taught, up to 1:25, in order to ensure maximum conversion of the formaldehyde. Example 10 of Snapp U.S. Pat. Nos. 3,573,702 and 3,701,798 teaches that a 1:3 molar ratio gave formaldehyde conversions of 34 to 45%. U.S. Pat. Nos. 3,574,703; 3,845,106; 3,928,458 to Hagemeyer, et al. teach the preparation of alpha, beta-unsaturated aldehydes by the vapor phase condensation of saturated aldehydes with at least two hydrogen atoms attached to the alpha carbon with formaldehyde in the presence of an unmodified silica gel catalyst. The activity and effectiveness of the catalysts are taught as functions of their pore volume and surface area. A 3:1 ratio of saturated aldehyde to formaldehyde is taught to obtain formaldehyde conversions of 35 to 45%, and selective yields based on formaldehyde consumed ranged from 88 to 94%.
Olefin oxidation processes for preparation of unsaturated aliphatic aldehydes are known. U.S. Pat. No. 3,437,690 to Young, et al. teaches a process for preparing acrolein which comprises reacting in the vapor phase propylene and oxygen in the presence of a catalyst comprising a calcined mixture of an oxide of arsenic, a molybdochromic heteropoly acid and a carrier. The oxide of arsenic can be alone, or together with an oxide of chromium, manganese, iron or boron. Mole ratio of olefin to oxygen can range from 1:0.2 to 1:10, preferably from 1:0.3 to 1:8. Conversions of propylene to acrolein are taught as within the range of from 3.4 to 16.4% with yields based on propylene within the range of 9.4 to 45.2%. U.S. Pat. No. 3,359,309, also to Young, teaches a similar process for olefin oxidation to acrolein using a catalyst comprising an arsenic oxide, a heteropoly acid of molybdenum containing manganese on a carrier. Conversions based on propylene ranged from 5.2 to 18.4%, and yields based on propylene consumed ranged from 14.4 to 61%.
Accordingly, a number of processes using basic catalysts for the condensation of two aldehydes have been taught heretofore. Other processes have been taught for the oxidation of olefins using an oxide of arsenic. However, the processes and catalysts taught heretofore suffer from disadvantages which are greatly minimized in the process of the instant invention. For instance, the processes taught in U.S. Pat. Nos. 2,639,295; 3,574,703; 3,845,106; and 3,928,458 are inferior to the present invented process in that formaldehyde conversions are low when the second aldehyde concentration is low, that a molar ratio of at least 3:1 is required for conversions of 35 to 45%, based on formaldehyde consumed. The processes taught in U.S. Pat. Nos. 3,359,309 and 3,437,690 are also inferior to the process of the instant invention. Conversions of olefin taught in U.S. Pat. Nos. 3,359,309 and 3,437,690 are within the range of from 3.4 to 18.4%.
An object of the present invention is to provide a process for making unsaturated aldehydes from formaldehyde and other aldehydes. A further object is to provide a process for making acrolein. Another object is to provide a process for making methacrolein. Other objects will appear hereinafter.
Quite unexpectedly, it has been found that a catalyst comprising an AMS-1B borosilicate crystalline molecular sieve having the following composition in terms of mole ratios of oxides: EQU 0.9.+-.0.2M.sub.2/n O:B.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O
where M is at least one cation, preferably hydrogen, n is the valence of the cation, Y is a value within the range of 4 to about 600, and Z is a value within the range of 0 to about 160, and providing a specific X-ray diffraction pattern, performs in a much superior manner for the present process with respect to conversion and selectivity relative to previously taught catalysts. Whereas previously taught catalyst formulations usually require a basic metal on silica or alumina substrates, the catalyst of the instant invented process is a borosilicate crystalline molecular sieve catalyst. Yield and selectivity are also improved over previously taught catalysts. The improved process has several unexpected results. Whereas previously taught processes result in low formaldehyde-based yields of alpha, beta-unsaturated aldehydes when the ratio of aldehyde to formaldehyde is low, such as 1:1, the aldehyde:formaldehyde ratio for the process of the present invention is 1:1 to 20:1, preferred is 1:1 to 10:1, more preferred is 1:1, with consequent economic advantage. Also, in the olefin process, substantial amounts of other products, mainly acrylic acid, often are formed from the olefin when the olefin oxidation process is used.